Carbon nanotube field emission based x-ray pixel beam array micro-RT system Carbon nanotube (CNT) field emission (FE) technology has been successfully used to develop novel radiographic imaging systems to meet the current and anticipated needs in both cancer biology research and medical application. To date, few works exist that explore the feasibility of this unique nanotechnology for radiation delivery devices. There is a growing need for ultra-high spatial and temporal resolution image-guided small animal irradiation and researchers today are struggling to meet the challenge using conventional technologies. The need for high-resolution small animal research tools is expected to grow drastically in the near future as new biomarker and biosensor agents, many are nanotechnology-based, coming out of the research and development pipeline for preclinical study for both intended and unintended effects including radiation- drug interaction. Our ultimate goal is to develop a nanotechnology based micro-CT-RT system that is capable of unprecedented temporal (<1ms) and spatial (<1mm) resolution small-animal image-guided intensity-modulated irradiation. The x-ray pixel beam array technology allows individual control of each of the pixel beams and thus the system electronically, not mechanically, defines radiation field shape and forms intensity modulation. Such feature is especially attractive for high-resolution small animal irradiation due to their extreme small scale and rapid organ motion. The specific goal for this exploratory R21 application is to demonstrate the feasibility of carbon nanotube field emission technology based x-ray pixel beam array micro-RT device. We have developed a prototype CNT FE based micro-CT scanner capable 30micron spatial resolution and 10ms temporal resolution. We hypothesize that the proposed micro-CT- RT system can deliver radiation to small-animal models in ways analogous or even superior to the state of the art radiotherapy received by human cancer patients today. Successful implementation of the micro-CT-RT system can significantly advance small- animal model studies integral to the development of new radiosensitizers, and radioprotectors, cancer cell detection or prognosis biomarkers for humans. The specific aims of the proposed three-year research are SA 1: Monte Carlo simulation and hardware based micro-RT system design;SA 2: Single array micro-RT system fabrication, SA 3: Prototype micro-RT system commissioning for small animal irradiation. The research project uses nanotechnology to develop novel image-guided radiation delivery tools for basic cancer research using small animal models. Currently, small animal irradiation technology is far behind the cancer research need. The proposed system promises to deliver small animal irradiation analogous to the state of the art radiotherapy for human and thus it will enable new and more clinically relevant animal model study.